Updates! Panel on order

A project log for LiFePO4wered/Solar1

A complete LiFePO4 based solar power supply for IoT devices

Patrick Van OosterwijckPatrick Van Oosterwijck 04/21/2017 at 23:572 Comments

I decided to use the Hackaday Prize 2017 as motivation to try and finally push this project to production! :)

I've had a unit outdoors in my #SoundBeacon project through the Colorado winter. We didn't have a very severe winter, so it wasn't a great test, but it seemed to work fine. I never saw the battery voltage go below 3.2V.

I've incorporated some changes based on what I've learned from testing the #LiFePO4wered/18650. I've gone to a bigger, higher current Schottky diode, and a newer, higher current MOSFET that I also intend to use in the #LiFePO4wered/Pi+. I hope to streamline my operations by trying to standardize components across projects. I also added a lot of thermal vias near the power components, especially the Schottky diode, to pull heat to the ground plane. With these changes, I hope that the system will be capable of 3A charge and load currents. To accommodate this, I also changed the thermal fuse on the output. The updated schematic is available in the files section.

If I did all my calculations correctly, the thermal protection system should be able to work with 10K NTC thermistors with B value between 3450 and 3950 (this seems to be some sort of "standard" in battery packs... I wish they'd ACTUALLY pick a standard resistance and B value instead). The battery will stop charging and the heater will kick in when the temperature falls below -3.1 to 0.2 degrees C. Charging will resume when the temperature rises above -2.5 to 0.7 degrees C. On the high temperature end, charging will stop when the temperature goes above 58 to 63 degrees C and will resume when the temperature falls below 52 to 57 degrees C.

I decided I need to get many more prototypes into the field to build confidence in the system. So I designed a panel so I can build a good number:

It's a small panel designed to fit within the 10x10 cm limits of Elecrow's Special Offer. So I will be getting 10 panels of 6 PCBs and I intend to use Tinkermill's TM245P pick-and-place machine to build these myself, since there are no difficult, small pitch components.

They are not officially for sale, but I had one customer very helpfully offer to buy some (at reduced "prototype" price) and test them in his devices. Thanks much Will! I want to encourage anyone else who has a need for a solar power supply to do so as well. The more field test data I can collect, the better!


Roman wrote 05/30/2017 at 14:42 point

Any chance to buy prototypes?

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Patrick Van Oosterwijck wrote 05/30/2017 at 16:50 point

Yes, I have about 50 prototypes built now and you can buy them.  Did you get my reply to your email last week?  I have versions with different current limits for charge current so if you could let me know if you want 0.5A, 1.93A, 2.35A or 3A charge current limit by email that would be great.

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